This invention relates generally to electrical connectors, and more particularly to bushings or connectors for use with tank-type electrical transformers.
Bushings or connectors currently used with tank-type electrical transformers, such as those known as low voltage bushings, generally comprise multi-piece assemblies made up of a molded epoxy bushing and associated conductor elements. Such an epoxy bushing is normally of an appropriate cross-section and size to meet mounting requirements, while the associated conductor normally extends through the epoxy bushing and usually includes specially-shaped end portions such as spade terminals, eyebolt connectors, or the like. Such an insulating epoxy molded bushing, however, in addition to providing insulative properties, also has been required to provide mechanical and structural properties since it is the primary means of securing the bushing or connector assembly to the tank wall. Thus it has been necessary to manufacture such epoxy bushings in elaborate shapes, using relatively expensive epoxy molding compounds, while still providing adequate structural strength. Needless to say, in many cases this delicate balance has proven to be very difficult to achieve.
Accordingly, it is a principal object of the present invention to provide an improved transformer bushing which in addition to furnishing the requisite conductive and insulative properties, does so by using a minimum amount of insulating material, that is, only that amount necessary to provide the insulative properties. Thus a more reliable bushing may be provided wherein the conducting material, rather than the more fragile insulating material, furnishes the required mechanical and structural properties.
In general, the transformer bushing assembly according to the present invention comprises a conducting member which provides the required shape and necessary mechanical and structural strength, and an insulating layer which is used only to provide the necessary insulating properties. The bushing assembly is made primarily, although not exclusively, for use with tank-type electrical transformers and is adapted to be inserted through an opening of predetermined cross-sectional dimension in the wall of the tank to provide electrical connection of the transformer with an external conductor. The bushing assembly is comprised of a conductor adapted to extend through the opening in the tank wall having a first connector portion for providing an electrical connection to the transformer, a second connector portion for providing an electrical connection to the external conductor, and a securing portion having a cross-sectional dimension greater than the predetermined cross-sectional dimension of the opening in the tank wall, for securing the bushing assembly to the wall of the tank. The bushing assembly further comprises a coating of dielectric material on the securing portion, which may be of substantially uniform thickness for insulating the conductor from electrical conduction with the wall, and securing means cooperative with the securing portion of the conductor for securing the bushing assembly to the wall, but maintaining insulation of the conductor from electrical conduction with the wall. In the two preferred embodiments described herein, the conductor may either be secured to the wall of the associated transformer tank by an externally mating clamp assembly having a similar dielectric layer thereon, or may include threads formed on its inside portion for engaging an insulated internally threaded securing member. It should of course be appreciated that these securing methods may be interchanged or modified without departing from the fair meaning of the present invention. Appropriate sealing and gasket materials are also provided.
In the one preferred embodiment described herein, the conductor includes a rod portion adapted to extend through the opening in the wall for providing a first rod end interior of the tank for connection to the transformer and a second rod end exterior of the tank for providing an electrical connection to the external conductor, and also includes a plate portion secured to the rod portion intermediate the ends thereof having a cross-sectional dimension greater than the predetermined cross-sectional dimension of the opening in the tank wall, for securing the bushing assembly to the wall of the tank. The bushing assembly further comprises a coating of dielectric material on the plate portion, which may be of substantially uniform thickness, for insulating the conductor from electrical conduction with the wall, and a clamping member having an opening therethrough for receiving one of the rod ends and being adapted to clamp the plate portion to the wall of the transformer to secure the bushing assembly to the wall but maintaining insulation of the conductor from electrical conduction with the wall.